/proc/buddyinfo

Each column of numbers represents the number of pages of that order which are available. In the example below, there are 7 chunks of 2 ^ 0 * PAGE_SIZE available in ZONE_DMA, and 12 chunks of 2 ^ 3 * PAGE_SIZE available in ZONE_NORMAL, etc...

This information can give you a good idea about how fragmented memory is and give you a clue as to how big of an area you can safely allocate.